During Electronic Road Pricing (ERP) hours, foreign cars without an in-vehicle unit are also levied a fixed ERP charge of $5 a day.

VEP, however, does not apply on weekends, public holidays, and after 5pm to before 2am on weekdays.

The new charge translates to a cost increase of at least 14 per cent for Malaysian drivers entering Singapore.

SIM University economist Walter Theseira said Singapore's reciprocal charge should be seen as "encouraging the Malaysian authority to bear in mind the consequences of its actions on its own citizens" when it introduces any foreign levy.

"As a sovereign state, we have to take a stand," he said. "We must not be seen as an easy source of revenue."